my brother was (and still is) definately the 'golden boy' of the family as a whole, even though he is a drug-addled lazy broccoli. he is on his thrid marriage, treats his kids and wife like crap, grows drugs in his attic, crashes his car because he is stoned all the time and is generally a waste of space.
i only have one child, so he has always been my favourite! i deliberately only had one because i was so young (17), had a crap childhood myself and didn't think i would cope well with more than that. i'm gald i did because we have always been skint and had to work loads, so he has had the focus of our attention and had a reasonable life so far - not spoilt, but he has turned out into a well rounded young man and i've no idea how i managed it (as i had such a bad example of parenting myself).
i can't imagine how things would have turned out if i'd had more, but i know i would have struggled and probably been a more rubbish parent as a result - possibly leading to the continuation of bad family dynamics and children who hated me. i quite like having one who i get on with and our relationship is changing as he matures into a young man.
on the subject of the op - my best friend's family (with 3 kids) definately has a favourite and they all suffer from the 'typical' oldest/youngest/middle child syndromes...and each of the parent has a favourite with my best mate being left out. i don't think anybody does it on purpose, but you can't always get on with everybody, can you? as a wise man once said: 'they f*ck you up, your mum and dad...' x